U.S. patent application number 10/017624 was filed with the patent office on 2002-06-06 for safety clutch for electrical hand-held tool.
Invention is credited to Bongers-Ambrosius, Hans-Werner, Hellmann, Peter, Kristen, Ferdinand.
Application Number | 20020066632 10/017624 |
Document ID | / |
Family ID | 7665425 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020066632 |
Kind Code |
A1 |
Kristen, Ferdinand ; et
al. |
June 6, 2002 |
Safety clutch for electrical hand-held tool
Abstract
A safety clutch for an electric hand-held tool and including a
rotor (8), an anchor disc (9) frictionally engageable with the
rotor (8) for transmitting a torque there-between, a stationary
axial stop (13) for limiting the air gap (s) between the rotor and
the anchor disc and engageable by the anchor disc under an axial
reserved pre-stress applied to the anchor disc (g); and a
stationary electromagnetic coil (11) provided on a side of the
rotor (8) remote from the anchor disc (9) and coaxial with the
rotor (8) for generating a rotationally symmetrical magnetic flux
(.phi.) for attracting of the anchor disc (g) to magnetic poles
(12a, 12b) associated with the rotor (8).
Inventors: |
Kristen, Ferdinand;
(Gilching, DE) ; Bongers-Ambrosius, Hans-Werner;
(Munich, DE) ; Hellmann, Peter; (Obermeitingen,
DE) |
Correspondence
Address: |
David Toren
SIDLEY AUSTIN BROWN & WOOD LLP
875 Third Avenue
New York
NY
10022
US
|
Family ID: |
7665425 |
Appl. No.: |
10/017624 |
Filed: |
November 30, 2001 |
Current U.S.
Class: |
192/17C ;
192/18B; 192/84.96 |
Current CPC
Class: |
F16D 2121/14 20130101;
F16D 2121/22 20130101; B25D 16/003 20130101; F16D 2123/00 20130101;
F16D 67/06 20130101; B25D 2211/003 20130101; B25D 2250/145
20130101; B25F 5/00 20130101; F16D 2027/008 20130101; F16D 59/02
20130101; F16D 27/112 20130101 |
Class at
Publication: |
192/17.00C ;
192/18.00B; 192/84.96 |
International
Class: |
F16D 067/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2000 |
DE |
100 59 747.5 |
Claims
What is claimed is:
1. A safety clutch for an electric hand-held tool, comprising a
rotor (8); an anchor disc (9) frictionally engageable with the
rotor (8) for transmitting a torque therebetween and spaced from
the rotor (8) by an air gap (5) in a disengagement position of the
anchor disc (9); a stationary axial stop (13) for limiting the air
gap (5) and engageable by the anchor disc under an axial reserved
pre-stress applied to the anchor disc (9); and a stationary
electromagnetic coil (11) provided on a side of the rotor (8)
remote from the anchor disc (9) and coaxial with the rotor (8) for
generating a rotationally symmetrical magnetic flux (.phi.) for
attracting of the anchor disc (9) to magnetic poles (12a, 12b)
associated with the rotor (8) to provide for a frictional
engagement of the anchor disc (9) with the rotor (8).
2. A safety clutch according to claim 1, wherein the axial stop
(13) is formed of a gliding material, and wherein the anchor disc
(9) forms only a linear contact with the stop (13).
3. A safety clutch according to claim 1, wherein the axial stop
(13) is formed as an annular member.
4. A safety clutch according to claim 1, further comprising an
axially prestressed spring (14) for applying the reserved prestress
to the anchor disc (9).
5. A safety clutch according to claim 4, wherein the spring (14) is
axially prestressed for applying the reserved prestress of from 1
to 5 N.
6. A safety clutch according to claim 1, wherein the air gap (5)
amounts from 0.3 to 0.5 mm.
7. A safety clutch according to claim 1, wherein the magnetic poles
(12a, 12b) are formed as pole shoes extending between the anchor
disc (9) and the rotor (8) and radially spaced from each other.
8. A safety clutch according to claim 7, wherein the rotor (8) is
formed as a cup-shaped member narrowly surrounding the
electromagnetic coil (11) from three sides.
9. A safety clutch according to claim 1, wherein the rotor (8) is
provided on a driving side of a torque transmission means, and the
anchor disc (9) is provided on a driven side of the torque
transmission means.
10. A safety clutch according to claim 1, further comprising a
controllable, radially displaceable brake element (10) with which
the rotor (8) cooperates.
11. A safety clutch according to claim 10, wherein the brake
element (10) is formed as one of small, electro-magnetically
controlled brake shoe and electromagnetically controlled braking
hand.
12. A safety clutch according to claim 10, wherein the brake
element (10) has a friction surface (17) engageable with a radially
outer surface (15) of the rotor (8).
13. A safety clutch according to claim 12, wherein the radially
outer surface (15) of the rotor (8) is provided with a nitride
layer (16).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a safety clutch for an
electrical hand-held tool with a rotatable working tool and which
separates, under critical operational conditions, the rotational
energy-supplying electric motor from the remainder of the power or
torque transmission chain. In particular, the present invention
relates to a safety clutch for a hammer drill.
[0003] 2. Description of the Prior Art
[0004] Electrical hand-held tools, such as hammer drills, are
usually driven by a rapidly rotatable electric motor that, as a
result, stores a lot of the rotational energy due to its large mass
moment of inertia. In order to protect the electrical tool user
under critical conditions, in particular in case of hooking of the
working tool, from an unpermissible deflection of the electrical
hand-held tool, either the drive energy should be cut off
sufficiently rapidly or the power transmission chain between the
rotational energy storing, electric motor and the working tool
should be sufficiently quickly broken. In large power electrical
hand-held tools, the drive energy cannot be cut-off sufficiently
rapidly without the use of additional means to that end.
[0005] For breaking a power transmitting chain, a clutch, which is
formed as a safety clutch, is incorporated into the power
transmitting chain. EP 666 148 discloses an electrically controlled
electromagnetic clutch which breaks the power transmitting chain,
in case of an accident, very rapidly. This clutch, under normal
operational conditions, provides for force transmission as a result
of static friction generated by an electrically controlled press-on
force.
[0006] German Publication DE 21 10 609 discloses an electrically
controlled magnetic clutch-brake combination including a driven
side rotor and a driving side, axially resiliently prestressed
anchor disc, and a stationary electromagnetic coil provided on a
side of the rotor remote from the anchor disc and coaxial with the
rotor for generating a rotationally symmetrical magnetic flux for
attracting of the anchor disc to magnetic poles associated with the
rotor to provide for a frictional engagement of the anchor disc
with the rotor for frictionally transmitting a torque
therebetween.
[0007] European Publication EP 893 616 discloses use of a
functioning like a brake, friction disc of a magnetic clutch-brake
combination and which is arranged in the drive chain.
[0008] European Publication EP-0 537 202 also discloses an
electro-magnetically actuated clutch-brake combination.
[0009] European Publication EP-0 947 721 discloses a clutch the
engaging surface of which is hardened with a nitride.
[0010] German Publication DE 38 28 854 discloses a clutch-brake
combination with radially displaceable, operating brake shoes.
[0011] An object of the present invention is to provide compact
electromagnetic clutch capable of transmitting a large torque.
[0012] Another object of the present invention is to provide a
safety clutch-brake combination with an electrically controlled,
active braking of the rotor.
SUMMARY OF THE INVENTION
[0013] This and other objects of the present invention, which will
become apparent hereinafter, are achieved by providing a safety
clutch including a rotor, an anchor disc frictionally engageable
with the rotor for transmitting a torque therebetween and spaced
from the rotor by an air gap in a disengagement position of the
anchor disc, stationary axial stop for limiting the air gap and
engageable by the anchor disc under an axial reserved prestress
applied to the anchor disc, and a stationary electromagnetic coil
provided on a side of the rotor remote from the anchor disc and
coaxial with the rotor for generating a rotationally symmetrical
magnetic flux for attracting of the anchor disc to magnetic poles
associated with the rotor to provide for a frictional engagement of
the anchor disc with the rotor.
[0014] Providing, according to the present invention, an axial
stop, which limits the gap between the anchor disc and the rotor in
the disengagement condition of the anchor disc and which becomes
engaged by the anchor disc under an axial reserved prestress,
insures a sufficiently rapid backspringing of the anchor disc that
insures a quick disengagement, a necessary characteristic of a
safety clutch.
[0015] Advantageously, the stop, which is formed as an annular
member, is made of a gliding material such as, e.g., red brass,
with the anchor disc forming with the stop advantageously only a
linear contact in the disengagement position of the anchor
disc.
[0016] Advantageously, the axial reserved prestress is applied by
an axially prestressed spring which is, preferably, formed as a
leaf spring and is arranged within the ring shaped anchor disc. The
spring applies a prestress in a range of 1-5 N. The spring has a
mass of about 45 g and a stroke within 0.5 mm.
[0017] Advantageously, the gap has a width of about 0.3-0.5mm. This
gap insures a free rotation of the not exactly axially rotatable
rotor and/or anchor rod and provides for a sufficient flux density
that insures obtaining a necessary magnetic force for overcoming
the reserved prestress.
[0018] Advantageously, the anchor disc and the rotor are formed
rotationally symmetrically with respect to each other and are
coaxial with each other, with two axially oriented pole shoes
formed therebetween. Thereby, when they approach each other, the
density of magnetic flux increases more rapidly than when only one
axial pole shoe is provided. As a result, upon engagement, the
transmitted torque, which is determined by the normal friction
force, is greater than when one pole shoe is used.
[0019] Advantageously, the rotor is provided on the driving side of
the power transmission chain, and the anchor disc is provided on
the driven side of the power transmission chain. As a result,
during disengagement, because of the small mass of the anchor disc,
a small reserved rotational energy is required.
[0020] Advantageously, the rotor is formed as a cup member narrowly
surrounding the electromagnetic coil from three sides, which
permits to achieve a high magnetic flux density.
[0021] Advantageously, the rotor has a radial, cylindrical outer
surface a normal to which oriented transverse to the rotational
axis does not cause generation of an axial counterforce when the
surface is subjected to a compression force.
[0022] Advantageously, the radial, cylindrical outer surface
cooperates with an innerfriction surface of the radially
displaceable, controllable brake element to provide for a
controllable active braking of the rotor.
[0023] Advantageously, the radially outer surface of the rotor,
which is formed of a soft magnetic material with a predetermined
hardness, is hardened by a gas nitriding process, with the
thickness of the nitride layer in a range from 0.003 mm to 0.01 mm.
This permits to have more than 10,000 braking actions without the
wear of the soft material of the rotor. Advantageously, a small
increase of the diameter of the rotor, as a result of providing a
nitride layer from 0.008 to 0.02, does not lead to any relevant
increase of the rotor diameter, which insures a high accuracy of
the rotor dimensions.
[0024] Advantageously, the brake element is formed as a small,
electromagnetically controlled brake shoe or brake band. As a
result, an active braking of the connected with the rotor, electric
motor, which continues to rotate after disengagement, takes place
in a hand-held tool within a narrow free space.
[0025] The novel features of the present invention, which are
considered as characteristic for the invention, are set forth in
the appended claims. The invention itself, however, both as to its
construction and its mode of operation, together with additional
advantages and objects thereof, will be best understood from the
following detailed description of preferred embodiment, when read
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS:
[0026] The drawings show:
[0027] FIG. 1 a side, partially cross-sectional view of an
electrical hand-held tool with a safety clutch according to the
present invention; and
[0028] FIG. 2 a cross-sectional view of a clutch-brake combination
forming the safety clutch for the electrical hand-held tool.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] An electrical hand-held tool 1 according to the present
invention, which is shown in FIG. 1, includes a housing 3 with a
chuck for receiving a working tool 2, a percussion mechanism 4
located in the housing 3, an electric motor 5 and a drive gear 6,
with both being located in the housing 3, and a safety clutch 7
arranged in a power flow from the electric motor 5 to the drive
gear 6.
[0030] The safety clutch 7, a cross-sectional view of which is
shown in FIG. 2, is formed, according to the invention, as a
clutch-brake combination. The clutch-brake combination includes a
rotatable rotor 8, an associated rotatable and axially
displaceable, within a limited range, anchor disc 9, and a brake
element 10 stationary secured in the housing 3. The anchor disc 9,
which is provided on a rotor side and is coaxial with the rotor 8,
is attracted or pulled to magnetic poles 12a, 12b, which are
provided on the rotor 8, by a rotationally symmetrical magnetic
flux .phi. which is generated by an electromagnetic coil 11
stationary secured in the housing 3. The anchor disc 9, being
attracted to the rotor 8, provides for frictional torque
transmission. In its disengaged condition, which is shown in FIG.
2, the anchor disc 9 forms with the rotor 8 a small gap S of 0.4
mm. The gap S is limited by an annular stop 13 stationary secured
in the housing 3 and coaxial with the rotor 8 and the anchor disc
9. In its disengaged condition, the anchor disc 9 abuts the stop 13
under a reserved prestress, forming a linear contact therewith. On
its bottom side, which is drivingly associated with the drive gear
6, the anchor disc 9 is provided with a leaf spring 14. The rotor
8, which is formed as a cup-shaped member, narrowly surrounds the
electromagnetic coil 11 and has its drive side, remote from the
anchor disc 9, associated with the electric motor 5. The rotor 9
has a radially outer cylindrical surface 15 which is covered with a
nitride layer 16 having a thickness of 0.007 mm. The cylindrical
surface 16 of the rotor 8 cooperates with a radially inner friction
surface 17 of the brake element 10 that is formed as a radially
displaceable brake shoe. The frictional engagement of the
cylindrical surface 15 of the rotor 8 with the friction surface 17
is electromagnetically controlled.
[0031] Though the present invention was shown and described with
references to the preferred embodiments, such are merely
illustrative of the present invention and are not to be construed
as a limitation thereof, and various modifications of the present
invention will be apparent to those skilled in the art. It is,
therefore, not intended that the present invention be limited to
the disclosed embodiments or details thereof, and the present
invention includes all variations and/or alternative embodiments
within the spirit and scope of the present invention as defined by
the appended claims.
* * * * *